THE RAT AS AN ANIMAL-MODEL FOR TOTAL HIP-REPLACEMENT ARTHROPLASTY

Dogs, goats, and sheep are the most commonly used animals in studies of total hip replacement (THR) arthroplasty. However, the development of a small, laboratory animal model could have significant economic and housing advantages over these models when studying the long-term systemic effects of chronic mechanically functional implants. A THR was designed and fabricated with a cobalt-alloy (F-75) femoral and UHMWPE acetabular component for PMMA-cemented implantation in the rat. Mature Sprague-Dawley rats (n = 18) were maintained at a constant weight (450 g) and were trained to walk on a low-speed (6 m/min), horizontal treadmill, 15 min/day, 5 days/week. Each animal was randomly assigned to one of three surgical groups: functional, nonfunctional, and sham. The functional and nonfunctional groups underwent identical procedures, except that in the nonfunctional group the femoral head was placed so as to prevent articulation with the socket in the acetabular component. The sham procedure consisted of exposing and opening the joint capsule and the iliac wing without luxating the femoral head or severing the ligamentum teres. In addition, half of the animals in each group resumed exercising on the treadmill at 1 week after surgery. The implants were recovered at 2 months after surgery. The results show that the surgical procedure is feasible in the rat, the postoperative recovery was typical of that for THR, and the rats were able to resume their exercising regimens. Radiographic evaluation revealed that the majority of the sham and the nonfunctional animals had luxated hips, while the majority of the functional animals had reduced hips. Histological results were typical of THR in other species. The success of the surgical model suggests that the rat may be a feasible, reduced-cast alternative to other lab species in systemic, long-term THR studies.